Diseases caused by viruses are the main obstacle to papaya production on a global scale. More than 45 viruses have been reported in tropical and subtropical regions. However, only the Papaya Ringspot Virus (PRSV) and the virus complex that causes the Meleira disease are considered threats to papaya production.
"A few years ago, we carried out evaluations in plantations in all the provinces of the northwest and the northeast and confirmed the presence of symptoms similar to those caused by viruses," stated Dariel Cabrera Mederos, Conicet researcher at the Plant Pathology and Agricultural Modelling Unit and INTA's Institute of Plant Pathology.
In Argentina, papaya is mainly grown in the subtropical region that includes the provinces of Salta, Jujuy, Chaco, Corrientes, Formosa, and Misiones. The area planted with papayas in the country has increased over the last decade because of this crop's economic benefits, mainly associated with its value in the national market and its profits in the industry.
According to the INTA researcher, during their tour in the NOA, they observed "mosaic symptoms in leaves similar to those induced by viruses, but which were not consistent with the viruses that had been reported." He also said that the samples collected were subjected to different analyses and revealed their association with a new potexvirus that has not been previously reported worldwide called papaya virus X.
This virus is transmitted mechanically on papaya and was found in most of the areas inspected in Salta and Jujuy.
PRSV causes mosaic, leaf deformation, and fruit banding. Papaya virus X induces intense mosaic on leaves, but no symptoms on fruits. The virus associated with the complex that causes Meleira causes the fruits to spontaneously exudate latex, which generates its characteristic symptom after its oxidation. The high incidence and severity of symptoms observed in the field led researchers to conclude that they could affect crop yields.
"We have not carried out direct studies to determine the effects on yields, but we know that the incidence reaches 100% during the crop's first year," Cabrera Mederos stated. Furthermore, "the rapid spread of this disease has made it difficult to establish new plantations."
In Brazil, for example, after seeing the damage caused by the Meleira-associated complex, producers have opted to destroy their crops to prevent the disease from spreading.
Preliminary research results corroborate that the disease is transmitted mechanically. Thus, researchers suggest producers carry out preventive management, such as disinfecting the tools used in plots and implementing disinfection protocols when entering recently established plantations.
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